RDMA/bnxt_re: Fix a double free in bnxt_qplib_alloc_res

In bnxt_qplib_alloc_res, it calls bnxt_qplib_alloc_dpi_tbl().  Inside
bnxt_qplib_alloc_dpi_tbl, dpit->dbr_bar_reg_iomem is freed via
pci_iounmap() in unmap_io error branch. After the callee returns err code,
bnxt_qplib_alloc_res calls
bnxt_qplib_free_res()->bnxt_qplib_free_dpi_tbl() in the fail branch. Then
dpit->dbr_bar_reg_iomem is freed in the second time by pci_iounmap().

My patch set dpit->dbr_bar_reg_iomem to NULL after it is freed by
pci_iounmap() in the first time, to avoid the double free.

Fixes: 1ac5a404

 ("RDMA/bnxt_re: Add bnxt_re RoCE driver")
Link: https://lore.kernel.org/r/20210426140614.6722-1-lyl2019@mail.ustc.edu.cn
Signed-off-by: Lv Yunlong <lyl2019@mail.ustc.edu.cn>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Acked-by: Devesh Sharma <devesh.sharma@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>